The invention relates to underwater excavating apparatus of the type generally disclosed in my U.S. Pat. No. 3,919,791 issued Nov. 18, 1975, which is incorporated herein by reference. It is directed particularly to apparatus for excavating difficult-to-dig material such as, for example, Carolina marl, hard clays, and tightly packed coal fines, and removing it to a dry land location. Previously, I have used a disc-type chipper in conjunction with dredging apparatus of the type employing a conventional cutterhead for the purpose of chipping up brush and tree growth ahead of the dredging cutterhead to prevent it from fouling the cutterhead.
The present invention utilizes a rapidly rotating disc-type cutterhead as the excavating head and mounts it for 180.degree. rotation so that the continuously powered cutterhead is able to literally cut its way to a reversed position in which it can take a return path cut at a lower level. At the same time a material collecting chamber is provided rearwardly of the disc cutterhead, leading to a suction pipe, and pump vanes are provided on the disc-type cutterhead to literally "supercharge" the suction pump conventionally provided on dredges to remove the slurry collected to a remote location.
It is to be understood that it is contemplated that the dredge boom may preferably be swung in transverse or sidewise arcs to take successive cuts by stepping the dredge forwardly alternatively about a pair of rearwardly located anchoring spuds as disclosed in my U.S. Pat. No. 3,777,375, issued Jan. 28, 1972 (also incorporated herein by reference), or may be swung with the dredging hull about a tail section as disclosed in my U.S. Pat. No. 3,919,791.
One of the prime objects of the present invention is to provide underwater dredging apparatus for difficult-to-excavate materials wherein a rotary disc cutter is connected to a dredge pump in a manner which will permit it to be power turned end-for-end in 90.degree. steps separated by a lowering step so that it may be employed to cut or excavate material on a continuous basis.
Another object of the invention is to provide a dredging system of the character described in which the cutter develops a pumping action which aids and, in a sense, "supercharges," the slurry pump carried by the dredge vessel.
Still another object of the invention is to provide a dredging system of the character described which requires relatively low boom swing forces while cutting material which is considered extremely difficult, if not impossible, to cut or dredge, the present cutterhead being of a type which cuts a thin slice of material and pulls it away from the body of material being excavated rather than putting the material in compression while digging it.
A correlative object of the invention is to provide a construction of the type described wherein the dredging of difficult-to-excavate material can, because of the low loading forces generated, proceed at a greatly accelerated pace, with resultant lower costs and vastly increased capacity.
Still another object of the invention is to provide a dredge system which can pulverize the material to a far greater extent than known systems where that is desirable.
Still another object of the invention is to provide a construction of the character described which essentially uses a dual pump system, in which a first pump "crams" the conventional pump used to remove slurry material, and permits it to operate much more efficiently and to handle far greater capacities by volume of solid material.
Still a further object of the invention is to provide a dredging system which pulverizes the material to a far greater extent than conventional excavating systems, with the result that the material is easier to remove and plugging problems are largely obviated.